1. Field of the Invention
The present invention relates to a semiconductor device fabrication method.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2008-85304 relates to a method of fabricating a MOS photoelectric conversion device. This reference has disclosed a technique by which the gate of an amplifier MOS transistor in a pixel is connected to a floating diffusion by a shared contact plug. The shared contact technique is advantageous in downsizing semiconductor devices.
Japanese Patent Laid-Open No. 2008-85304 does not mention the relationship between the conductivity type or impurity concentration of a diffusion region to be connected by the shared contact plug and the conductivity type or impurity concentration of the gate of a MOS transistor.
When two regions to be connected by the shared contact plug have opposite conductivity types, the shared contact plug must be brought into ohmic contact with both of the two regions. However, no reference has discussed this subject. It is difficult to obtain a highly integrated, low-noise, high-speed semiconductor device unless ohmic contacts with these two regions are achieved.